1. Field of Invention
The invention relates to a dynamic bearing manufacturing method and in particular to a manufacturing method for dynamic grooves in the dynamic bearing.
2. Related Art
The bearing is one of the important components of a motor. Extending the life and reducing the operating noise of the motor are important considerations in choosing and designing the bearing.
Ball bearings and roller bearings are not suitable in many products due to the noise caused by the rolling balls and rollers and the bearing damage caused by axial or radial forces. Fluid dynamic bearings (FDBs) are invented for these reasons. FDBs have a plurality of herringboned grooves at an inner wall of the bearing to concentrate the stress so that the bearing can be lubricated and the motor can rotate smoothly. Compared to the ball bearing and the roller bearing, the FDB has lower noise and non-abrasion because the rotating shaft do not contact the bearing. Thus, the life of the FDB may be extended.
However, the herringboned grooves of the FDB need higher processing precision, which complicates the manufacturing process and increases the manufacturing cost. Referring to FIGS. 1A and 1B, a conventional processing method of the FDB includes the following steps. Firstly, the herringboned grooves are formed by scrapping the inner wall 121 of a bearing 12 with a multi-axle processor 11. The multi-axle processor 11 has four knives rotating and traverses along the inner wall 121 of the bearing 12 in a counterclockwise (or clockwise) direction. Then, when the multi-axle processor 11 reaches a turning point P, the knives of the multi-axle processor 11 rotates and traverses along the inner wall 121 in a clockwise (or counterclockwise) direction so as to form the herringboned grooves on the inner wall 121 of the bearing 12. Because after the herringboned groove is formed, the knives 111 have to return to the original position, it is necessary to constrains the number of the grooves to be even. However, the number of the grooves can not be optimized due to the limitation of the processing, and thus the FDB can not achieve the optimal stress satisfying actual requirements.
Referring to FIGS. 2A to 2C, another conventional processing method of a FDB is to position a shaft 13 with the herringboned grooves on a central axial hole 122 of the bearing 12 (as shown in FIG. 2A), and then to exert a force F from an exterior wall 124 of the bearing 12 to compress the bearing 12 (as shown in FIG. 2B) so that the inner wall 121 of the bearing 12 conforms to the shaft 13. Therefore, the herringboned grooves are formed on the inner wall 121 of the bearing 12 by a printing method (as shown in FIG. 2C). However, because the grooves are made by pressuring, the wall thickness of the bearing 12 can not be very thick, and the thinner wall thickness may incur shrink of the axial hole.
Referring to FIGS. 3A to 3C, another processing method of the FDB is to position a hollow tooling 141 having the herringboned grooves, which are arranged in a protruding pattern, within the central axial hole 122 of the bearing 12 (as shown in FIG. 3A), and then to coercively dilate the hollow tooling 141 by using a dilating element 142 so that the herringboned grooves of the hollow tooling 141 intervene the inner wall 121 of the bearing 12 (as shown in FIG. 3B) and then the herringboned grooves are transferred and printed on the inner wall 121 (as shown in FIG. 3C). However, the coercive introduction of the dilating element 142 to the hollow tooling 141 rapidly wears the hollow tooling 141 and the dilating element 142. If the hollow tooling 141 and the dilating element 142 are worn and not changed promptly, the precision of the herringboned grooves will be imprecise and reduce the reliability of the bearing 12.
As mentioned above, since the conventional processing methods of the FDB have disadvantages such as the limited number of herringboned grooves, the limited thickness of the bearing or the limited processing precision, the design and manufacture. are complicated and the efficiency of the FDB is reduced. Therefore, it is an important subject to provide a manufacturing method of the bearing to solve those problems.